The purpose of the work is to study long-term adverse effects possibly following a delivery with cesarean section. Effects on subsequent fertility, ectopic pregnancies and on malformations of subsequent children having been studied using U.S. data. Subsequent fertility is studied by comparing women having had a cesarean section to those having had a vaginal delivery in their first pregnancy using data from the 1982 National Survey of Family Growth. Effect on ectopic pregnancies is studied by comparing the past delivery history of women having had ectopic pregnancy to that of women having had a live birth or a spontaneous abortion. The data source is fetal and live birth certificates in Upstate New York. Effects on malformations are studied by comparing the malformation rates of children whose mothers's have had a previous cesarean section to that of children whose mothers have had a previous vaginal delivery. The data source is the Collaborative Perinatal Project. Many different types of problems, both for the mother and infant, in the subsequent pregnancies have been studied using the data in the Swedish Birth Register. Future plans include linking this data to hospital discharge register to study problems not related to pregnancies ending in birth.